FIG. 3 is a cross-sectional view showing a prior art long wavelength transmitter OEIC described in pages 190 and 191 of Second Optoelectronics Conference (OEC' 88) Technical Digest. In FIG. 3, reference numeral 1 designates a semi-insulating InP substrate. A semiconductor laser 17 and a field effect transistor 18 (hereinafter referred to as FET) for driving the semiconductor laser 17 are integrated on the substrate 1. An n type InGaAsP layer 14 to which an n side electrode 9 of the semiconductor laser is attached is disposed on the concave part of the InP substrate 1 which is formed by etching.
An n type InP cladding layer 2' is disposed on the n type InGaAsP layer 14. An InGaAsP active layer 3' is disposed on the ridge part of the cladding layer 2'. A p type InP cladding layer 4' is disposed on the active layer 3'. A current blocking layer 15 is disposed on the cladding layer 2' burying the ridge part. A contact layer 16 is disposed on the current blocking layer 15. A p side electrode 8 of the semiconductor laser is disposed on the contact layer 16 and an n side electrode 9 is disposed on a region of the n type InGaAsP layer 14 where the laminated-layers of the laser are not present. An undoped GaAs buffer layer 13 is disposed on a convex part of the substrate 1. An n type GaAs operating layer 5' is disposed on the buffer layer 13. A gate electrode 12 of the FET is disposed on the bottom of a recess groove formed on the operating layer 5'. A source electrode 10 and a drain electrode 11 are disposed on opposite sides of the recess groove.
Description is given of the operation hereinafter.
The n side electrode 9 of semiconductor laser 17 is connected with the source electrode 10 of FET 18 by wiring. The operations of the semiconductor laser 17 and the FET 18 are the same as those of the independent elements. More specifically, the driving current of semiconductor laser 17 is subjected to a modulation such as an interruption by a voltage applied to the gate 12 of FET 18 and the light output of semiconductor laser 17 is modulated correspondingly, thereby resulting in operation as a transmitter OEIC.
A method for manufacturing the transmitter OEIC of FIG. 3 is illustrated in FIGS. 4(a) to 4(i).
A portion of InP substrate 1 shown in FIG. 4(a) is etched away as shown in FIG. 4(b) to form a lower stage part on which the semiconductor laser 18 is to be produced. That is, in order to arrange the p side electrode 8 of semiconductor laser and the source/drain electrodes 10 and 11 of FET approximately on the same plane, the surface of substrate 1 on which the semiconductor laser comprising thick layers is to be formed is formed in a different plane from the surface on which the FET is to be formed. Then, as shown in FIG. 4(c), an n type InGaAsP layer 14 on which an electrode of the semiconductor laser is to be produced, an n type InP cladding layer 2', an InGaAsP active layer 3' and a p type InP cladding layer 4' are grown by liquid phase epitaxy (LPE), metal-organic chemical vapor deposition (MOCVD) or the like (first crystal growth). Then, unnecessary portions of cladding layer 2', active layer 3' and cladding layer 4' other than portions to be an active region of semiconductor laser are removed by photolithographic techniques and etching, resulting in a stripe-shaped mesa shown in FIG. 4(d). Thereafter, as shown in FIG. 4(e), a current blocking layer 15 and a contact layer 16 are grown by LPE (second crystal growth). Then, as shown in FIG. 4(f), unnecessary portions of the contact layer 16 and the current blocking layer 15 are removed by etching. Then, as shown in FIG. 4(g), a buffer layer 13 and a GaAs operating layer 5' of the FET are successively grown by molecular beam epitaxy (MBE) (third crystal growth). Then, as shown in FIG. 4(h), the recess portion of FET is formed by etching. Thereafter, as shown in FIG. 4(i), p side and n side electrodes 8 and 9 of semiconductor laser and the source, drain and gate electrodes 10, 11, 12 of FET are formed, thereby completing a transmitter OEIC.
As described above, three crystal growth steps are required for manufacturing the prior art long wavelength transmitter OEIC. More specifically, the first crystal growth step is for growing layers of the semiconductor laser, i.e., the n type InGaAsP layer 14, the n type InP cladding layer 2', the InGaAsP active layer 3' and the p type InP cladding layer 4', the second crystal growth step is for growing the current blocking layer 15 and the contact layer 16 after etching those layers 14, 2', 3' and 4' to form a ridge, and the third crystal growth step is for growing layers of the FET, i.e., the undoped GaAs buffer layer 13 and the n type GaAs operating layer 5'. So many crystal growth processes complicate the manufacturing process, resulting in a poor production yield and a high cost. Furthermore, in the manufacturing process, a step difference in the substrate 1 that is approximately equal to the entire thickness of the laser, i.e., 5 microns or more, inevitably arises. Such a step difference induces nonuniformity of in the photoresist films used in the photolithography process and, therefore, it is difficult to form a fine pattern FET. As a result, a high performance OEIC, for example, a high speed OEIC cannot be produced.